Occurrence data are being entered into a relational database using the software Access 2002. There are eight linked data tables containing information on taxonomy, localities, references, etc. A master table contains records corresponding to individual occurences of species at given localities at a given point in time. Thus, the database includes the following fields: Phylum, Class, Family, Genus, Species, Species Author, Collector, Locality of collection (Latitude, Longitude, City, County, etc.), Date of collection, Type of data source (i.e. museum, published literature, unpublished source, survey), Museum number for the specimen (for museum specimens), Reference (for literature and unpublished data), and numerous note fields. In addition, we produced a series of interrelated forms that serve as user-friendly interfaces for data entry.

While examining museum collections we have found that a considerable fraction (roughly 40 percent) of the museum material for the species we have looked at do not have precise dates of collection listed. This is especially true for the oldest specimens. However, the vast majority of these specimens have information indicating the collectors and/or the former collections to which the specimens belonged. We have therefore been able to estimate dates of collection for the majority of these specimens by gathering biographical information (birth, death, earliest and latest years of documented collection) for more than 230 individuals who have collected molluscs in Southern California, as well as recording the earliest and latest known dates of collection for specimens previously stored in more than 50 (mostly private) collections that are presently housed in major museums. The incorporation of these data into our main database and has significantly improved both spatial and temporal coverage of our database. As is the case for all of the data we collect, this information will be available through this website.

By linking the occurrence of each specimen to its museum number, we ensure that future changes in the taxonomic designations of species can be easily reflected in the database. This will also provide a way to double check the taxonomic identifications of specimens that may be anomalous in terms of occurrence or those that might indicate extensive local extinctions. Such ground truthing is somewhat more difficult for the literature data (although some papers do provide museum numbers).